The present invention relates to reflective radiation barriers and more particularly to a barrier having a housing with a base element embedded therein. The base houses a radiation emitter or transmitter and receiver or detector, all of which may be monolithic semiconductors built on a common substrate. The radiation may be light and the present invention will be discussed with respect to light emission. However, the present invention is not limited to light applications and may include other radiation wavelengths as will be discussed below.
Reflective or reflexive light barriers or an apparatus for detecting motion of an object may take many forms and applications as shown in the prior art. For example, application of the barriers may be for space detection, as well as tracking and automation systems. The barriers may frequently come in the form of miniature components and be applied in consumer and entertainment electronics. The barriers are increasingly used for monitoring mechanical device components such as video player load flaps and sleds of CD drives. Essential criteria for such applications include size, degree of miniaturization, and cost.
U.S. Pat. No. 3,842,263 sets out a photoelectric switching device wherein the light transmitter and the light receiver are each placed in separate, channel-shaped indentations of common cased body. The channel-shaped indentation associated with the light transmitter serves as a directional for the light emitted by the transmitter. The partition which runs between the two indentations avoids cross-talk between emitted light and the receiver.
German Patent DE 36 33 181 A1 sets out a reflected light barrier wherein the light transmitter and the light receiver are placed on a common semiconductor substrate. A free-standing screen, produced from the semiconductor substrate by an etching step, is provided for the optical separation of light transmitter and light receiver.
U.S. Pat. No. 3,697,762 sets out a light scanner having a partition between an LED (luminous source) and a photo element (light receiver) in order to avoid cross talk between the source and receiver.
German Patent DE 39 29 085 A1 sets out a reflex light barrier using LED""s as light transmitters.
Additional reflective light barriers and light scanners are described in the German patents DE 298 02 763 U1, DE 43 04 343 A1 and DE 28 24 583 C3, which set out input as well as output optics and are only marginally appropriate for miniaturization.
Still additional reflective light barriers are set out in U.S. Pat. Nos. 5,753,929 and 3,842,263; German Patents DE 43 37 005 A1, DE 39 29 085 A1 and DE 198 28 069 A1; European Patent Applications EP 0 786 839 A1 and EP 0 751 510 A2; and Japanese Abstract 09321597.
It is an advantage of the present invention to provide a reflective light barrier with a high degree of miniaturization potential at reduced costs. Herein, the light transmitter may be a vertically emitting semiconductor transmitter with a vertical resonator such as a vertical cavity surface emitting laser (VCSEL) or a resonant cavity light emitting diode (RCLED). Through use of a vertically emitting semiconductor transmitter with a vertical resonator, especially a VCSEL or RCLED, low beam divergence can be obtained. Accordingly, cross-talk between transmitter and receiver can be kept below a working tolerance of the present apparatus. As such, a partition is no longer necessary. In practice, a certain degree of cross-talk may be tolerated. The particular threshold may vary depending upon application and optical path length, reflectivity of the detected object, and the like. In addition, as VCSELs generally display a lower beam divergence than RCLEDs, the former may be applied where the latter divergence is unacceptably high.
By avoiding use of a free-standing partition which is common in the art, the possibility now exists for closer placement of the transmitter and receiver within the, present apparatus, A reflective light barrier with overall smaller dimensions is therefore possible. A preferred design of the invention includes a maximum lateral casing size equal to or less than 2.5 mm. Alternatively, the casing size may be smaller than 0.5 mm.
The light transmitter can be built from a multiple number of single light transmitter elements. The elements may, for example, be arranged in an uni-dimensional row or a two-dimensional array. By optimizing the number of transmitter elements, the geometrical arrangement of the transmitters, the orientation of the transmitter-arrangement relative to the light receiver, the intensity of light, and other parameters, a minimization of cross-talking can be obtained for a select casing size and distance. Hence, cross talk may be minimized between transmitter and receiver.
A further reduction of cross-talk may be obtained via use of polarizers. In particular, a polarizer may be placed in the beam path incident upon the light receiver. Because the object location, beam source and receiving point are known, it will be known in advance what effect the detected object will have on the polarity of light reflected off it. As such, the polarizer placed on the receiver may be preselected so as to pass only light reflected by the object. Other light, including that emitted by the transmitter would not pass. As such, the effectiveness of the present apparatus increases and the need for a light partition between the transmitter and receiver is obviated. A second possibility may be the inclusion of a polarizer on the transmitter as well. Herein the transmitter polarizer may be at about 90 degrees to the receiver polarizer thereby again obviating the need for a barrier.
Still a further possibility includes the use of an optical filter. The filter may be a day light filter and/or a band pass filter. The filter may be placed in the incident beam path upstream from the light receiver in order to suppress stray day light. The usage of a day light filter is preferable if the emission wavelength of the light transmitter lies outside of the visible area (for example at approx. 1 xcexcm). Selection and use of a band pass filter may be effected such that its transmitted wavelength substantially corresponds to the emission wavelength of the light transmitter.
Still a further possibility includes use of a modulator to modulate the light transmitted by the light transmitter and a demodulator to distinguish between received, modulated reflected light and received, non-modulated stray light.
Still a further possibility includes use of an integrated circuit (IC) coupled with the light transmitter and/or the light receiver. The IC may be located in the casing and be provided according to a functional design of the invention. The integrated circuit can either comprise a driver switching circuit for the light transmitter as well as a scoring switching circuit. If the reflected light barrier is operated with modulated emission light, the integrated circuit can be additionally equipped with a driver-equipped with a modulator stage and scoring circuit-coupled to the demodulator.
The transmitter, receiver, and integrated circuit may be formed monolithically on a common semiconductor substrate thereby creating elements for an especially high degree of miniaturization.
The structure of the present invention may include a circular casing embedded in the base housing. The base may include at least four internally mounted surfaces having through holes and electrical contacts. Accordingly, the transmitter and receiver may be applied on the contact surface. The application may be electrical bonding as well as possible electrical cross bonding to one of the remaining contact surfaces. Such casings are standard in the art and may be produced by large scale manufacturing for the absorption of three luminescent diodes of the elementary colors green, red, blue, to be used as color picture point in a display. These casings may therefore be economical and may further contribute to an overall cost reduction of the present invention.
The invention is explained in greater detail below and by reference to exemplary embodiments shown in the drawings wherein like numerals refer to equivalent elements.